题 目：Effects of pressure, doping and electronic correlations in iron pnictide superconductors
报告人：Harald O. Jeschke (Junior Group leader, Institute for Theoretical Physics, Goethe-University Frankfurt)
We investigate the effects of the uniaxial tensile andcompressive stresses applied along a, b and a+b directions in BaFe2As2 and CaFe2As2 in the framework of ab initio density functional theory calculations. While the systems remain in the orthorhombic phase at moderate pressures, we observe an inversion of magnetism at a critical strain happening when the a and b axes approach the tetragonal condition. Furthermore, the doping-temperature-pressure phase diagrams of the 122 family of superconductors have been discussed intensively due to electronic nematicity above the structural and superconducting transition and the complex coupling between electronic and lattice degrees of freedom. We employ density functional theory to predict the structure of supercells of Ca1-xSrxFe2As2 and CaFe2 (As1-xPx)2. We then predict structural transitions of the doped compounds under pressure and compare to the parent compound. We carefully analyze the changes in the electronic structure caused by doping and stress.
We also performed charge self-consistent LDA+DMFT (density functional theory combined with dynamical mean field theory) calculations to study correlation effects on the Fermi surfaces of the iron pnictide superconductors LaFePO, LiFeP and LiFeAs. We find a distinctive change in the topology of the Fermi surface in LaFePO and LiFeP where a hole pocket with Fe dz$^2$ orbital character changes its geometry from a closed shape in LDA to an open shape upon inclusion of correlations. In LiFeAs correlations influence mostly the shape of the hole pockets. We discuss our results in the context of angle-resolved photoemission spectroscopy and de Haas van Alphen observations.
Dr. Harald O. Jescke received his Ph.D. degree from Freie University Berlin in June 2000. From Jan. 2002 to Feb.2004, he was a Emmy Noether fellow and postdoctoral associate in department of physics & astronomy, Rutgers university. From Mar. 2004, he became a Junior group leader in Institute for Theoretical Physics, JohannWolfgang Goethe-University, Frankfurt am Main. Dr. Jeschke has published over 70 papers in international research journals, including 1 Nature Materials, 11 Physical Review Letters, 1 JACS.